Alright kiddo, have you ever heard someone say things like "America is for Americans" or "Immigrants are taking away our jobs"? That's called nativism. Nativism is when people believe that only people who are born in America are true Americans, and that immigrants or people with different cultures or religions are bad for America. Some people who believe in nativism think that there are too many immigrants coming to America, and that it's hurting the country.
Nativism was really strong in America in the late 1800s and early 1900s, when a lot of people were immigrating to America from places like Italy, Ireland, and Eastern Europe. Some Americans were worried that these new immigrants wouldn't be able to fit in with American society. They were afraid that the immigrants would bring their own languages, religions, and cultures with them, and that this would create division in America.
To try to stop this, some people who believed in nativism started groups like the Know-Nothing Party and the Ku Klux Klan. These groups tried to limit how many new immigrants could come to America, and they worked to keep immigrants from becoming citizens. They also tried to keep people who weren't white or Protestant from coming to America.
Now, some people still believe in nativism today. They're worried about things like illegal immigration, and they believe that people who come to America should try to fit in with American culture as much as possible. But other people believe that America is a country of immigrants, and that diversity is one of the things that makes America great. They believe that everyone should be treated equally, no matter where they were born or what their religion is. So, that's what nativism is all about!